Transmission channel for ultrasound applications

ABSTRACT

A transmission channel configured to transmit high-voltage pulses and to receive echos of the high-voltage pulses includes a high voltage buffer, a voltage clamp and a switch. The voltage clamp may include clamping transistors and switching off transistors coupled together in series with body diodes in anti-series. The transmission channel may include a reset circuit configured to bias the transmission channel between pulses. The switch may include a bootstrap circuit.

BACKGROUND

1. Technical Field

The present disclosure relates to transmission channels.

The disclosure relates, but not exclusively, to transmission channelsfor ultrasound applications and the following description is made withreference to this field of application by way of illustration only.

2. Description of the Related Art

Sonography or ultrasonography is a system of medical diagnostic testingthat uses ultrasonic waves or ultrasounds and is based on the principleof the transmission of the ultrasounds and of the emission of echo andis widely used in the internistic, surgical and radiological field.

The ultrasounds normally used are, for example, between 2 and 20 MHz infrequency. The frequency is chosen by taking into consideration thathigher frequencies have a greater image resolving power, but penetrateless in depth in the subject under examination.

These ultrasounds are being normally generated by a piezoceramic crystalinserted in a probe maintained in direct contact with the skin of thesubject with the interposition of a suitable gel (being suitable foreliminating the air between probe and subject's skin, allowing theultrasounds to penetrate in the anatomic segment under examination). Thesame probe is able to collect a return signal or echo, which may besuitably processed by a computer and displayed on a monitor.

The ultrasounds that reach a variation point of the acoustic impedance,and thus for example an internal organ, are partially reflected and thereflected percentage conveys information about the impedance differencebetween the crossed tissues. It is to be noted that, the big impedancedifference between a bone and a tissue being considered, with thesonography it is generally not possible to see behind a bone, whichcauses a total reflection of the ultrasounds, while air or gas zonesgive “shade”, causing a partial reflection of the ultrasounds.

The time employed by an ultrasonic wave for carrying out the path ofgoing, reflection and return is provided to the computer, whichcalculates the depth wherefrom the echo has come, thus identifying thedivision surface between the crossed tissues (corresponding to thevariation point of the acoustic impedance and thus to the depthwherefrom the echo comes).

Substantially, an ultrasonographer, in particular a diagnostic apparatusbased on the ultrasound sonography, may essentially comprise threeparts:

-   -   a probe comprising at least one transducer, for example of the        ultrasonic type, which transmits and receives an ultrasound        signal;    -   an electronic system that drives the transducer for the        generation of the ultrasound signal or pulse to be transmitted        and receives an echo signal of return at the probe of this        pulse, processing in consequence the received echo signal; and    -   a displaying system of a corresponding sonography image        processed based on the echo signal received by the probe.

The word transducer generally indicates an electric or electronic devicethat converts a type of energy relative to mechanical and physicalquantities into electric signals. In a broad sense, a transducer issometimes defined as any device that converts energy from one form toanother, so that this latter can be re-processed, for example by men orby other machines. Many transducers are both sensors and actuators. Anultrasonic transducer usually comprises a piezoelectric crystal that issuitably biased for causing its deformation and the generation of theultrasound signal or pulse.

A typical transmission channel or TX channel being used in theseapplications is schematically shown in FIG. 1.

The transmission channel 1 comprises an input logic 2 that drives, incorrespondence with an input bus BUS_(IN), a level shifter 3, in turnconnected to a high voltage buffer block 4. The high voltage bufferblock 4 is electrically coupled between pairs of high voltage referenceterminals, respectively higher voltage reference terminals HVP0 and HVP1and lower voltage reference terminals HVM0 and HVM1, and has a pair ofinput terminals, INB1 and INB2, connected to the level shifter 3, aswell as a pair of output terminals, OUTB1 and OUTB2, connected to acorresponding pair of input terminals, INC1 and INC2 of a clamping block5.

Furthermore, the clamping block 5 is connected to a clamp voltagereference terminal PGND and has an output terminal corresponding to afirst output terminal HVout of the transmission channel 1, in turnconnected, through an anti-noise block 6, to a connection terminal Xdcrfor the transducer to be driven through the transmission channel 1.

A high voltage switch 7 is electrically coupled between the connectionterminal Xdcr and a second output terminal LVout of the transmissionchannel 1. This high voltage switch 7 is able to transmit an outputsignal being at the output of the anti-noise block 6 to the secondoutput terminal LVout during the receiving step of the transmissionchannel 1.

It is to be noted that the switch 7 may be a high voltage one since,during the transmission step of the transmission channel 1, a signalbeing on the connection terminal Xdcr is a high voltage signal althoughthe switch 7 is off. When this switch 7 is instead on, i.e., during thereception step of the transmission channel 1, the signal Xdcr isgenerally at a voltage value next to zero since the piezoelectrictransducer connected to the transmission channel 1 is sensing smallreturn echoes of ultrasound pulse signals, as shown in FIG. 2.

Typically, an ultrasonic transducer transmits a high voltage pulse ofthe duration of a few us, and listens for reception of the echo of thispulse, generated by the reflection on the organs of a subject underexamination, for the duration of about 250 us, to go back to thetransmission of a new high voltage pulse.

For example, a first pulse IM1 and a second pulse IM2 are transmittedwith a peak to peak excursion equal, in the example shown, to 190 Vppwith reception by the transducer of corresponding echoes shown in FIG. 2and indicated with E1 and E2.

The high voltage switch 7 is shown in greater detail in FIG. 3A, whileits equivalent circuit according to working conditions (ON) is shown inFIG. 3B.

The high voltage switch 7 comprises a first switching transistor MS1 anda second switching transistor MS2, being electrically coupled, in seriesto each other, between the connection terminal Xdcr and the secondoutput terminal LVout of the transmission channel 1 and havingrespective control or gate terminals connected, at the turning-on of theswitch 7 itself, to a first and to a second supply voltage referenceterminals, VDD_M and VDD_P respectively. FIG. 3A also shows theequivalent diodes, DS1 and DS2, of the switching transistors, MS1 andMS2, as well as their gate-source capacitances, Cg1 and Cg2respectively.

The first capacitance Cg1 of the first switching transistor MS1 isconnected between the corresponding gate terminal, in turn connected tothe first supply voltage reference terminal VDD_M and a first switchingnode XS1, corresponding to a source terminal of the first switchingtransistor MS1. Similarly, the second capacitance Cg2 of the secondswitching transistor MS2 is connected between the relative gateterminal, in turn connected to the second supply voltage referenceterminal VDD_P and a second switching node XS2, corresponding to asource terminal of the second switching transistor MS2.

As shown in the equivalent circuit of FIG. 3B, when the high voltageswitch 7 is on and thus the gate terminals of the switching transistorsMS1and MS2 are connected to the first VDD_M and to the second supplyvoltage reference terminal VDD_P as indicated in FIG. 3A (which in FIG.3B, for sake of simplicity, have been shown as a single referencevoltage, for example, ground, being these first and second supplyvoltage references), these switching transistors behave as respectiveresistances R1 and R2, that are electrically coupled between theconnection terminal Xdcr and the second output terminal LVout of thetransmission channel 1 (the second output terminal LVout coinciding withthe second switching node XS2) and interconnected in correspondence withthe first switching node XS1.

According to these conditions, the first capacitance Cg1 is connectedbetween the first connection node XS1 and the first supply voltagereference VDD_M, while the second capacitance Cg2 is connected betweenthe second connection node XS2 and the second supply voltage referenceVDD_P. The first and second supply voltage references are fixedsupplies, and are shown for sake of simplicity in FIG. 3B as a singlereference voltage, the ground GND. This parallel capacitance introducesa strong mitigation of the signal at the input of the high voltageswitch 7, i.e., of the signal at the output of the transmission channel1 after the anti-noise block 6.

In general, then, the switch 7 should be a high voltage one so as not tobreak itself during the transmission step but it is in practice onalways with low voltages during the receiving step.

Further, the high voltage buffer block 4 comprises a first branchcomprising a first buffer transistor MB1 and a first buffer diode DB1,being electrically coupled, in series to each other, between a firsthigher voltage reference terminal HVP0 and a buffer central node XBc, aswell as a second buffer diode DB2 and a second buffer transistor MB2,electrically coupled, in series to each other, between the buffercentral node XBc and a first lower voltage reference terminal HVM0. Thefirst and second buffer transistors, MB1 and MB2, have respectivecontrol or gate terminals in correspondence with a first XB1 and with asecond inner circuit node XB2 of the high voltage buffer block 4 andconnected to, and driven by, a first DRB1 and a second buffer inputdriver DRB2, in turn connected to the level shifter 3 in correspondencewith the first and second input terminals, INB1 and INB2, of the highvoltage buffer block 4.

The high voltage buffer block 4 also comprises, in parallel to the firstbranch, a second branch in turn comprising a third buffer transistor MB3and a third buffer diode DB3, being electrically coupled, in series toeach other, between a second higher voltage reference terminal HVP1 andthe buffer central node XBc, as well as a fourth buffer diode DB4 and afourth buffer transistor MB4, electrically coupled, in series to eachother, between the buffer central node XBc and a second lower voltagereference terminal HVM1. The third and fourth buffer transistors, MB3and MB4, have respective control or gate terminals in correspondencewith a third XB3 and a fourth inner circuit node XB4 of the high voltagebuffer block 4 and connected to, and driven by, a third DRB3 and afourth buffer input driver DRB4, in turn connected to the first XB1 andto the second inner circuit node XB2 and then to the first DRB1 and tothe second buffer input driver DRB2, respectively, as well as to a firstOUTB1 and to a second output terminal OUTB2.

In the example of the figure, the first and third buffer transistors,MB1 and MB3, are high voltage P-channel MOS transistors (HV Pmos) whilethe second and fourth buffer transistors, MB2 and MB4, are high voltageN-channel MOS transistors (HV Nmos). Moreover, the buffer diodes, DB1,DB2, DB3 and DB4, are high voltage diodes (HV diode).

The clamping block 5 has in turn a first INC1 and a second inputterminal INC2, respectively connected to the first OUTB1 and secondoutput terminal OUTB2 of the high voltage buffer block 4.

The clamping block 5 comprises a first clamp driver DRC1 connectedbetween the first input terminal INC1 and a control or gate terminal ofa first clamp transistor MC1, in turn electrically coupled, in serieswith a first clamp diode DC1, between the clamp voltage referenceterminal PGND, for example a ground, and a clamp central node XCc. Thefirst clamp transistor MC1 and the first clamp diode DC1 areinterconnected in correspondence with a first clamp circuit node XC1.

The clamping block 5 also comprises a second clamp driver DRC2 connectedbetween the second input terminal INC2 and a control or gate terminal ofa second clamp transistor MC2, in turn electrically coupled, in serieswith a second clamp diode DC2, between the clamp central node XCc andthe clamp voltage reference terminal PGND. The second clamp transistorMC2 and the second clamp diode DC2 are interconnected in correspondencewith a second clamp circuit node XC2.

The clamp central node XCc is also connected to the first outputterminal HVout of the transmission channel 1, in turn connected to theconnection terminal Xdcr through an anti-noise block 6 comprisingrespective first and second anti-noise diodes, DN1 and DN2, connected inantiparallel, i.e., by having the anode terminal of the first diodeconnected to the cathode terminal of the second diode and vice versa,between the first output terminal HVout and the connection terminalXdcr.

In the example of the figure, the first clamp transistor MC1is a highvoltage P-channel MOS transistor (HV Pmos) while the second clamptransistor MC2 is a high voltage N-channel MOS transistor (HV Nmos).Moreover, the clamp diodes, DC1 and DC2, are high voltage diodes (HVdiode) while the anti-noise diodes, DN1 and DN2, are low voltage diodes(LV diode).

The clamping block 5 is also shown in FIG. 4, in the case of a clampingoperation to a ground voltage reference GND, i.e., during the receivingstep of the transmission channel 1. It is to be noted that the clampingto the ground voltage reference GND generally should be ensured alsowhen the load is mainly capacitive. In this case, the output terminal ofthe transmission channel should generally be brought back to this groundvalue after the transmission.

Furthermore, the clamping to the ground is generally desirable inapplications in which the high voltage wave form to be transmitted,besides oscillating between a positive value of high voltage and anegative value of high voltage, stays for determined periods of time atthe ground value.

Also the anti-noise block 6 is indicated too, being connected betweenthe first output terminal HVout and the connection terminal Xdcr of thetransmission channel 1.

This FIG. 4 also shows the equivalent diodes, DMC1 and DMC2, of theclamp transistors, MC1 and MC2, respectively, the first and second clampinput drivers, DRC1 and DRC2, being connected between a first clampsupply voltage reference terminal and a second clamp supply voltagereference terminal, higher VDD_P and lower VDD_M, respectively, and theground GND, whereto also the clamp central node XCc is connected.

BRIEF SUMMARY

It is evident from the scheme of FIG. 4, that, when the clamping block 5is on, the first output terminal HVout is at a voltage value,corresponding to the value of ground voltage GND plus or minus a diodevoltage and the connection terminal Xdcr to a value of ground voltageGND plus or minus two diode voltages.

In theory, the optimal working condition would have this first outputterminal HVout at a value equal to the ground GND, condition in whichthe distortions of the transmitted signal by the transmission channel 1are minimum. In fact, the real working conditions of the clamping block5 above illustrated show worsening in the performances of secondharmonic, especially under conditions of low supply voltages.

In case of connection of a load of great value, a high current cancirculate through the high voltage clamp diodes DC1 and DC2, chargingthe junction intrinsic capacitances of the same diodes and causing amalfunction.

During the reception step of the transmission channel 1, it is generallynecessary to wait that the connection terminal Xdcr is at zero. Leakagecurrent of the first output terminal HVout, caused by the noiseintroduced by the charges being in the clamp diodes DC1 and DC2, causesa raising of the voltage value also on this connection terminal Xdcr andthus a receiving disturbance.

For example, once the high voltage buffer block 4 has been turned onagain, the first output terminal HVout does not immediately respondsince most of the current supplied by this high voltage buffer block 4is used for the discharge of the junction capacitances of the clampdiodes DC1 and DC2, precharged during the clamping step. Thismalfunction is particularly felt in case of short pulses.

Moreover, during the reception step in which the clamping block 5 is onand the connection terminal Xdcr has a voltage value next to but notequal to the ground GND, a leakage current could charge the first outputterminal HVout at a voltage higher than the threshold voltage of theanti-noise diodes, DN1 and DN2, of the anti-noise block 6 and, inconsequence, disturb a reception on the connection terminal Xdcr.

After a cycle of pulses, the anode terminals of the first DB1 and of thethird buffer diode DB3 and the cathode terminals of the second DB2 andof the fourth buffer diode DB4 stabilise at a voltage depending ondifferent factors such as the value of a supply voltage, the value ofthe inner capacitances, which one and how many transistors are used forthe switching, the switching frequency etc.

This means that each successive pulse train may find a different and nondefined initial condition.

By changing the initial status also the output wave form is modifiedwith the consequence that, the input control being identical, it ispossible to obtain different outputs. In other words, the wave form ofthe output signal is function of the input signals and of the initialcondition resulting from the switches previously occurred thus creatinga sort of “memory effect”.

An embodiment facilitates providing desirable and predictable switchinginitial conditions in a transmission channel clamping circuit.

In an embodiment, high voltage diodes are connected to the inner nodesof the high voltage buffer block of the transmission channel to bias itscondition between a pulse cycle and another one so as to reduce thememory effect of this buffer block, as well as of associating the clamptransistors to corresponding high voltage MOS transistors able to closethemselves when the clamping circuit is active and likewise able tosustain positive and negative high voltages when instead the clampingcircuit is not active and the transistors are in open configuration andof realising a switching circuit of the type comprising switchingtransistors and provided with bootstrap circuitry configured to drivethe control terminals of these switching transistors with a following ofa signal at the input of the switching circuit itself towards itsoutput.

In an embodiment, a transmission channel comprises:

-   -   a high voltage buffer block comprising buffer transistors and        respective buffer diodes, being electrically coupled between        respective voltage reference terminals, said high voltage buffer        block having at least one first and one second output terminal,        as well as a buffer central node;    -   a clamping circuit being connected to a first output terminal of        said transmission channel and having at least one first and one        second input terminal connected to said first and second output        terminals of said high voltage buffer block, a first and a        second clamp circuit node, as well as a clamp central node        connected to said buffer central node;    -   an anti-noise block being connected between said first output        terminal and a connection terminal of said transmission channel;        as well as    -   a switching circuit being electrically coupled between said        connection terminal and a second output terminal of said        transmission channel    -   characterised in that    -   said clamping circuit comprises a clamping core in turn        including at least one first and one second clamp transistor,        connected to said central node and to said first and second        clamp circuit node, respectively, through diodes connected to        prevent the body diodes of said clamping transistors from        conducting and having respective control terminals, as well as        at least one first switching off transistor connected to said        output terminal and to said first clamp transistor and a second        switching off transistor connected to said output terminal and        to said clamp transistor, said first and second clamp        transistors being high voltage MOS transistors of complementary        type and said first and second switching off transistors being        high voltage MOS transistors of complementary type connected to        said first and second clamp transistors by having the respective        equivalent or body diodes in anti-series so as to close        themselves when said clamping circuit is active and to sustain        positive and negative high voltages when said clamping circuit        is not active;    -   said reset circuit comprising diodes and being electrically        coupled between circuit nodes of said high voltage buffer block        and of said clamping circuit, said circuit nodes being in        correspondence with conduction terminals of said transistors        comprised into said high voltage buffer block and into said        clamping circuit, and    -   said switching circuit comprising at least one first and one        second switching transistor which are high voltage MOS        transistors of complementary type being electrically coupled, in        series to each other and by having respective equivalent or body        diodes in anti-series, between said connection terminal and said        second output terminal, as well as at least one bootstrap        circuit connected to respective first and second control        terminals of said at least one first and one second switching        transistor, as well as to respective first and second voltage        reference terminals and having values of parasite capacitances        between said first and second control terminals and at least one        first and one second bootstrap node of at least one order of        magnitude lower with respect to the gate-source capacitances of        said at least one first and one second switching transistor.

Embodiments may comprise, for example, the following supplementary andoptional characteristics, taken alone or in combination.

In an embodiment, said first switching off transistor may be a highvoltage P-channel MOS transistor and said second switching offtransistor may be a high voltage N-channel MOS transistor.

In an embodiment, said transmission channel may further comprise adriving circuit connected to respective control terminals of said firstand second clamp transistors and of said first and second switching offtransistors and suitable for closing said first and second switching offtransistors when said clamping circuit is active.

In an embodiment, said driving circuit may comprise a first and a seconddriving transistor, being electrically coupled, in a crossed way,between said control terminals of said first and second clamptransistors, and respective control terminals of said first and secondswitching off transistors.

In an embodiment, said first driving transistor may be electricallycoupled between said control terminal of said first clamp transistor anda control terminal of said second switching off transistor and saidsecond driving transistor may be electrically coupled between a controlterminal of said first switching off transistor and said controlterminal of said second clamp transistor.

In an embodiment, said first and second driving transistors may haverespective control terminals connected to said clamp central node.

In an embodiment, said clamping core may be connected at the input to aninput driver block comprising a first and a second driver electricallycoupled between a first supply voltage reference terminal and a secondsupply voltage reference terminal and having respective output terminalsconnected to said control terminals of said first and second clamptransistors.

In an embodiment, said first clamp transistor may be a high voltageN-channel MOS transistor and said second clamp transistor may be a highvoltage P-channel MOS transistor.

In an embodiment, said first and second driving transistors may be highvoltage MOS transistors of a type similar to said first and secondswitching off transistors.

In an embodiment, said first switching off transistor may be a highvoltage N-channel MOS transistor and said second switching offtransistor may be a high voltage P-channel MOS transistor.

In an embodiment, said high voltage buffer block comprises at least onefirst branch in turn including a first buffer transistor and a firstbuffer diode, being electrically coupled, in series to each other,between a first higher voltage reference terminal and a buffer centralnode and interconnected in correspondence with a first memory node, aswell as a second buffer diode and a second buffer transistor, beingelectrically coupled, in series to each other, between said buffercentral node and a first lower voltage reference terminal andinterconnected in correspondence with a second memory node, and saidreset circuit may comprise:

-   -   a first memory diode, being electrically coupled between said        first memory node and said first clamp circuit node; and    -   a second memory diode, being electrically coupled between said        second memory node and said second clamp circuit node.

In an embodiment, said first memory diode may have a cathode terminalconnected to said first memory node and an anode terminal connected tosaid first clamp circuit node and said second memory diode may have ananode terminal connected to said second memory node and a cathodeterminal connected to said second clamp circuit node.

In an embodiment, said first memory node may be connected to an anodeterminal of said first buffer diode and said first clamp circuit nodemay be connected to an anode terminal of said first clamp diode and saidsecond memory node may be connected to a cathode terminal of said secondbuffer diode and said second clamp circuit node may be connected to acathode terminal of said second clamp diode.

In an embodiment, said first memory node may be in correspondence with adrain terminal of said first buffer transistor and said second memorynode may be in correspondence with a drain terminal of said secondbuffer transistor.

Moreover, in an embodiment, said high voltage buffer block alsocomprises, in parallel to said first branch, a second branch in turnincluding a third buffer transistor and a third buffer diode, beingelectrically coupled, in series to each other, between a second highervoltage reference terminal and said buffer central node andinterconnected in correspondence with a third memory node, as well as afourth buffer diode and a fourth buffer transistor, being electricallycoupled, in series to each other, between said buffer central node and asecond lower voltage reference terminal and interconnected incorrespondence with a fourth memory node, and said reset circuit mayfurther comprise:

-   -   a third memory diode, being electrically coupled between said        third memory node and said first clamp circuit node; and    -   a fourth memory diode, being electrically coupled between said        fourth memory node and said second clamp circuit node.

In an embodiment, said third memory diode may have a cathode terminalconnected to said third memory node and an anode terminal connected tosaid first clamp circuit node and said fourth memory diode may have ananode terminal connected to said fourth memory node and a cathodeterminal connected to said second clamp circuit node.

In an embodiment, said third memory node may be connected to an anodeterminal of said third buffer diode and said first clamp circuit nodemay be connected to an anode terminal of said first clamp diode and saidfourth memory node may be connected to a cathode terminal of said fourthbuffer diode and said second clamp circuit node may be connected to acathode terminal of said second clamp diode.

In an embodiment, said third memory node may be in correspondence with adrain terminal of said third buffer transistor and said fourth memorynode may be in correspondence with a drain terminal of said fourthbuffer transistor.

In an embodiment, said high voltage buffer block may comprise respectivebuffer drivers connected to control terminals of said buffertransistors.

In an embodiment, said bootstrap circuit of said switching circuit maycomprise at least one first biasing generator electrically coupledbetween said first control terminal and said first bootstrap node, aswell as a second biasing generator electrically coupled between saidsecond bootstrap node and said second control terminal as first andsecond parasite capacitances of said bootstrap circuit.

In an embodiment, said at least one first and second biasing generatormay supply respective first and second biasing current.

In an embodiment, said bootstrap circuit further comprises a firstbootstrap transistor being electrically coupled, in series to a firstbootstrap resistive element, between said first control terminal of saidfirst switching transistor and said second bootstrap node, as well as asecond bootstrap transistor being electrically coupled, in series to asecond bootstrap resistive element, between said second control terminalof said second switching transistor and said first bootstrap node.

In an embodiment, said first bootstrap transistor may have a controlterminal connected to a first inner circuit node of said switchingcircuit, corresponding to a source terminal of said first switchingtransistor and said second bootstrap transistor may have a controlterminal connected to a second inner circuit node of said switchingcircuit, corresponding to a source terminal of said second switchingtransistor.

In an embodiment, said first bootstrap transistor may be a low voltageN-channel MOS transistor and said second bootstrap transistor may be alow voltage P-channel MOS transistor.

In an embodiment, said first and second bootstrap nodes may be connectedto said first and second voltage references, respectively.

In an embodiment, said values of parasite capacitances of said bootstrapcircuit may be of at least some orders of magnitude, preferably three,lower with respect to the gate-source capacitances of said at least onefirst and one second switching transistor.

In an embodiment, a transmission channel comprises: a clamp including: aclamp output; a clamp input configured to couple to a reference voltage;a first clamping transistor; a second clamping transistor; a firstswitching off transistor coupled between the output and the firstclamping transistor; and a second switching off transistor of the clampcoupled between the output and the second clamping transistor, wherein,the first and second clamping transistors are high-voltage MOStransistors of complementary types; the first clamping transistor iscoupled between the first switching off transistor and the input, thefirst clamping transistor and the first switching off transistor havingbody diodes coupled together in anti-series; and the second clampingtransistor is coupled between the second switching off transistor andthe input, the second clamping transistor and the second switching offtransistor having body diodes coupled together in anti-series; and areset block including: a first memory diode coupled to a conductionterminal of the first clamp transistor and configured to couple to aconduction terminal of a first transistor of a high-voltage buffer; anda second memory diode coupled to a conduction terminal of the secondclamp transistor and configured to couple to a conduction terminal of asecond transistor of the high-voltage buffer. In an embodiment, thetransmission channel further comprises: a switching circuit, having: aconnection terminal; an output terminal; first and second voltagereference terminals; first and second switching transistors electricallycoupled in series to each other, and having respective body diodescoupled in anti-series, between said connection terminal and said outputterminal, the first switching transistor having a first control terminaland the second switching transistor having a second control terminal;and a bootstrap circuit connected to the first and second controlterminals and to the first and second voltage references and including:first and second bootstrap nodes; a first parasitic capacitanceelectrically coupled between said first control terminal and the firstbootstrap node; and a second parasitic capacitance electrically coupledbetween said second control terminal and the second bootstrap node, thefirst and second parasitic capacitances having capacitance values of atleast one order of magnitude lower than gate-source capacitances of saidfirst and second switching transistors. In an embodiment, thetransmission channel further comprises: the high-voltage buffer; and ananti-noise block coupled between the clamp and the switching circuit. Inan embodiment, said first switching off transistor is a high voltageP-channel MOS transistor and said second switching off transistor is ahigh voltage N-channel MOS transistor. In an embodiment, thetransmission channel further comprises a driving circuit coupled tocontrol terminals of said first and second clamp transistors and of saidfirst and second switching off transistors and configured to generatedriving signals to close said first and second switching off transistorswhen said clamping circuit is active. In an embodiment, said drivingcircuit comprises: a first driving transistor coupled between thecontrol terminal of the first clamping transistor and the controlterminal of the second switching off transistor; and a second drivingtransistor coupled between the control terminal of the second clampingtransistor and the control terminal of the first switching offtransistor. In an embodiment, said first and second driving transistorshave respective control terminals connected to said clamp input. In anembodiment, the clamp comprises an input driver block, the controlterminal of the first clamping transistor is coupled to an output of afirst driver of the input driver block and the control terminal of thesecond clamping transistor is coupled to an output of a second driver ofthe input driver block. In an embodiment, said first clamping transistoris a high voltage N-channel MOS transistor and said second clampingtransistor is a high voltage P-channel MOS transistor. In an embodiment,said first driving transistor and the first switching off transistor areof a first MOS type and the second driving transistor and the secondswitching-off transistor are of a second MOS type complementary to thefirst MOS type. In an embodiment, the transmission channel furthercomprises the high-voltage buffer, wherein the high voltage bufferincludes at least one first branch having the first buffer transistorand a first buffer diode coupled in series between a first highervoltage reference terminal and a buffer central node, and a secondbuffer diode and the second buffer transistor coupled in series betweensaid buffer central node and a first lower voltage reference terminal.In an embodiment, said first memory diode has a cathode coupled to saidconduction terminal of the first buffer transistor and an anode coupledto said conduction terminal of the first clamp transistor, said secondmemory diode has an anode coupled to said conduction terminal of thesecond buffer transistor and a cathode coupled to said conductionterminal of the second clamp transistor, said first buffer diode has ananode coupled to the cathode of the first memory diode, said secondbuffer diode has a cathode coupled to the anode of the first memorydiode, the conduction terminal of the first buffer transistor is a drainterminal of the first buffer transistor and the conduction terminal ofthe second buffer transistor is a drain terminal of the second buffertransistor. In an embodiment, said high voltage buffer block includes asecond branch including a third buffer transistor and a third bufferdiode coupled in series between a second higher voltage referenceterminal and said buffer central node, and a fourth buffer diode and afourth buffer transistor coupled in series between said buffer centralnode and a second lower voltage reference terminal, and said reset blockcomprises: a third memory diode coupled between a conduction terminal ofthe third buffer transistor and the conduction terminal of the firstclamp transistor; and a fourth memory diode coupled between a conductionterminal of the fourth buffer transistor and the conduction terminal ofthe second clamp transistor, wherein said third memory diode has acathode coupled to said conduction terminal of the third buffertransistor and an anode coupled to said conduction terminal of the firstclamp transistor, said fourth memory diode has an anode coupled to theconduction terminal of said fourth buffer transistor and a cathodecoupled to said conduction terminal of the second clamp transistor, theconduction terminal of the third buffer transistor is a drain terminalof the third buffer transistor and the conduction terminal of the fourthbuffer transistor is a drain terminal of the fourth buffer transistor.In an embodiment, said high voltage buffer block comprises respectivebuffer drivers connected to control terminals of said buffertransistors. In an embodiment, said bootstrap circuit comprises: a firstbiasing generator electrically coupled between said first controlterminal of the first switching transistor and said first bootstrapnode; and a second biasing generator electrically coupled between saidsecond bootstrap node and said second control terminal of the secondswitching transistor, the first and second biasing generators includingthe first and second parasitic capacitances, respectively. In anembodiment, said bootstrap circuit further comprises: a first bootstraptransistor and a first bootstrap resistive element electrically coupledin series to each other between said first control terminal of the firstswitching transistor and said second bootstrap node; and a secondbootstrap transistor and a second bootstrap resistive elementelectrically coupled in series to each other between said second controlterminal of the second switching transistor and said first bootstrapnode, said first bootstrap transistor has a control terminalelectrically coupled to a source terminal of said first switchingtransistor and said second bootstrap transistor has a control terminalelectrically coupled to a source terminal of said second switchingtransistor. In an embodiment, said values of said parasitic capacitancesof said bootstrap circuit are of at least three orders of magnitudelower with respect to the gate-source capacitances of said first andsecond switching transistors.

In an embodiment, a transmission channel comprises: a clamp including: aclamp output; a clamp input configured to couple to a reference voltage;a first clamping transistor; a second clamping transistor; a firstswitching off transistor coupled between the output and the firstclamping transistor; and a second switching off transistor of the clampcoupled between the output and the second clamping transistor, wherein,the first and second clamping transistors are high-voltage MOStransistors of complementary types; the first clamping transistor iscoupled between the first switching off transistor and the input, thefirst clamping transistor and the first switching off transistor havingbody diodes coupled together in anti-series; and the second clampingtransistor is coupled between the second switching off transistor andthe input, the second clamping transistor and the second switching offtransistor having body diodes coupled together in anti-series; and aswitching circuit, including: a connection terminal; an output terminal;first and second voltage reference terminals; first and second switchingtransistors electrically coupled in series to each other, and havingrespective body diodes coupled in anti-series, between said connectionterminal and said output terminal, the first switching transistor havinga first control terminal and the second switching transistor having asecond control terminal; and a bootstrap circuit connected to the firstand second control terminals and to the first and second voltagereferences and including: first and second bootstrap nodes; a firstparasitic capacitance electrically coupled between said first controlterminal and the first bootstrap node; and a second parasiticcapacitance electrically coupled between said second control terminaland the second bootstrap node, the first and second parasiticcapacitances having capacitance values of at least one order ofmagnitude lower than gate-source capacitances of said first and secondswitching transistors. In an embodiment, the transmission channelfurther comprises: an anti-noise block coupled between the clamp outputand the connection terminal. In an embodiment, said first switching offtransistor is a high voltage P-channel MOS transistor and said secondswitching off transistor is a high voltage N-channel MOS transistor. Inan embodiment, the transmission channel further comprises a drivingcircuit coupled to control terminals of said first and second clamptransistors and of said first and second switching off transistors andconfigured to generate driving signals to close said first and secondswitching off transistors when said clamping circuit is active. In anembodiment, said driving circuit comprises: a first driving transistorcoupled between the control terminal of the first clamping transistorand the control terminal of the second switching off transistor; and asecond driving transistor coupled between the control terminal of thesecond clamping transistor and the control terminal of the firstswitching off transistor. In an embodiment, said bootstrap circuitcomprises: a first biasing generator electrically coupled between saidfirst control terminal of the first switching transistor and said firstbootstrap node; and a second biasing generator electrically coupledbetween said second bootstrap node and said second control terminal ofthe second switching transistor, the first and second biasing generatorsincluding the first and second parasitic capacitances, respectively. Inan embodiment, said bootstrap circuit further comprises: a firstbootstrap transistor and a first bootstrap resistive elementelectrically coupled in series to each other between said first controlterminal of the first switching transistor and said second bootstrapnode; and a second bootstrap transistor and a second bootstrap resistiveelement electrically coupled in series to each other between said secondcontrol terminal of the second switching transistor and said firstbootstrap node, said first bootstrap transistor has a control terminalelectrically coupled to a source terminal of said first switchingtransistor and said second bootstrap transistor has a control terminalelectrically coupled to a source terminal of said second switchingtransistor. In an embodiment, said values of said parasitic capacitancesof said bootstrap circuit are of at least three orders of magnitudelower with respect to the gate-source capacitances of said first andsecond switching transistors.

In an embodiment, a transmission channel comprises: a voltage clampincluding: a voltage clamp output; a first clamping transistor; and asecond clamping transistor; a reset block including: a first memorydiode coupled to a conduction terminal of the first clamp transistor andconfigured to couple to a conduction terminal of a first transistor of ahigh-voltage buffer; and a second memory diode coupled to a conductionterminal of the second clamp transistor and configured to couple to aconduction terminal of a second transistor of the high-voltage buffer;and a switching circuit, including: a connection terminal; an outputterminal; first and second voltage reference terminals; first and secondswitching transistors electrically coupled in series to each other, andhaving respective body diodes coupled in anti-series, between saidconnection terminal and said output terminal, the first switchingtransistor having a first control terminal and the second switchingtransistor having a second control terminal; and a bootstrap circuitconnected to the first and second control terminals and to the first andsecond voltage references and including: first and second bootstrapnodes; a first parasitic capacitance electrically coupled between saidfirst control terminal and the first bootstrap node; and a secondparasitic capacitance electrically coupled between said second controlterminal and the second bootstrap node, the first and second parasiticcapacitances having capacitance values of at least one order ofmagnitude lower than gate-source capacitances of said first and secondswitching transistors. In an embodiment, the transmission channelfurther comprises: the high-voltage buffer; and an anti-noise blockcoupled between the clamp and the switching circuit. In an embodiment,the transmission channel further comprises the high-voltage buffer,wherein the high voltage buffer includes at least one first branchhaving the first buffer transistor and a first buffer diode coupled inseries between a first higher voltage reference terminal and a buffercentral node, and a second buffer diode and the second buffer transistorcoupled in series between said buffer central node and a first lowervoltage reference terminal. In an embodiment, said first memory diodehas a cathode coupled to said conduction terminal of the first buffertransistor and an anode coupled to said conduction terminal of the firstclamp transistor, said second memory diode has an anode coupled to saidconduction terminal of the second buffer transistor and a cathodecoupled to said conduction terminal of the second clamp transistor, saidfirst buffer diode has an anode coupled to the cathode of the firstmemory diode, said second buffer diode has a cathode coupled to theanode of the first memory diode, the conduction terminal of the firstbuffer transistor is a drain terminal of the first buffer transistor andthe conduction terminal of the second buffer transistor is a drainterminal of the second buffer transistor. In an embodiment, said highvoltage buffer block includes a second branch including a third buffertransistor and a third buffer diode coupled in series between a secondhigher voltage reference terminal and said buffer central node, and afourth buffer diode and a fourth buffer transistor coupled in seriesbetween said buffer central node and a second lower voltage referenceterminal, and said reset block comprises: a third memory diode coupledbetween a conduction terminal of the third buffer transistor and theconduction terminal of the first clamp transistor; and a fourth memorydiode coupled between a conduction terminal of the fourth buffertransistor and the conduction terminal of the second clamp transistor,wherein said third memory diode has a cathode coupled to said conductionterminal of the third buffer transistor and an anode coupled to saidconduction terminal of the first clamp transistor, said fourth memorydiode has an anode coupled to the conduction terminal of said fourthbuffer transistor and a cathode coupled to said conduction terminal ofthe second clamp transistor, the conduction terminal of the third buffertransistor is a drain terminal of the third buffer transistor and theconduction terminal of the fourth buffer transistor is a drain terminalof the fourth buffer transistor. In an embodiment, said bootstrapcircuit comprises: a first biasing generator electrically coupledbetween said first control terminal of the first switching transistorand said first bootstrap node; and a second biasing generatorelectrically coupled between said second bootstrap node and said secondcontrol terminal of the second switching transistor, the first andsecond biasing generators including the first and second parasiticcapacitances, respectively. In an embodiment, said bootstrap circuitfurther comprises: a first bootstrap transistor and a first bootstrapresistive element electrically coupled in series to each other betweensaid first control terminal of the first switching transistor and saidsecond bootstrap node; and a second bootstrap transistor and a secondbootstrap resistive element electrically coupled in series to each otherbetween said second control terminal of the second switching transistorand said first bootstrap node, said first bootstrap transistor has acontrol terminal electrically coupled to a source terminal of said firstswitching transistor and said second bootstrap transistor has a controlterminal electrically coupled to a source terminal of said secondswitching transistor. In an embodiment, said values of said parasiticcapacitances of said bootstrap circuit are of at least three orders ofmagnitude lower with respect to the gate-source capacitances of saidfirst and second switching transistors. In an embodiment, the voltageclamp further comprises: a first clamping diode coupled between thefirst clamping transistor and the clamp output in anti-series with abody diode of the first clamping transistor; and a second clamping diodecoupled between the second clamping transistor and the clamp output inanti-series with a body diode of the first clamping transistor.

In an embodiment, a system comprises: means for generating high-voltagepulses; means for clamping a transmission channel output to a referencevoltage; means for biasing the means for clamping between pulses; andmeans for receiving pulse echos. In an embodiment, the means forclamping comprises: a clamp output; a clamp input configured to coupleto a reference voltage; a first clamping transistor; a second clampingtransistor; a first switching off transistor coupled between the outputand the first clamping transistor; and a second switching off transistorof the clamp coupled between the output and the second clampingtransistor, wherein, the first and second clamping transistors arehigh-voltage MOS transistors of complementary types; the first clampingtransistor is coupled between the first switching off transistor and theinput, the first clamping transistor and the first switching offtransistor having body diodes coupled together in anti-series; and thesecond clamping transistor is coupled between the second switching offtransistor and the input, the second clamping transistor and the secondswitching off transistor having body diodes coupled together inanti-series. In an embodiment, the means for biasing comprises: a firstmemory diode configured to couple to a conduction terminal of a firstclamp transistor and to a conduction terminal of a first transistor ofthe means for generating high-voltage pulses; and a second memory diodeconfigured to couple to a conduction terminal of a second clamptransistor and to a conduction terminal of a second transistor of themeans for generating high-voltage pulses. In an embodiment, the meansfor receiving pulse echos comprises: a connection terminal; an outputterminal; first and second voltage reference terminals; first and secondswitching transistors electrically coupled in series to each other, andhaving respective body diodes coupled in anti-series, between saidconnection terminal and said output terminal, the first switchingtransistor having a first control terminal and the second switchingtransistor having a second control terminal; and a bootstrap circuitconnected to the first and second control terminals and to the first andsecond voltage references and including: first and second bootstrapnodes; a first parasitic capacitance electrically coupled between saidfirst control terminal and the first bootstrap node; and a secondparasitic capacitance electrically coupled between said second controlterminal and the second bootstrap node, the first and second parasiticcapacitances having capacitance values of at least one order ofmagnitude lower than gate-source capacitances of said first and secondswitching transistors.

Characteristics and the advantages of various embodiments oftransmission channels will be apparent from the following descriptiongiven by way of indicative and non limiting example with reference tothe annexed drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In these drawings:

FIG. 1 schematically shows a transmission channel for ultrasoundapplications realised according to the prior art;

FIG. 2 schematically shows a first and a second ultrasound pulse used inan ultrasonic transducer;

FIG. 3A shows in greater detail a high voltage switch during a turn-onstep and being comprised within the transmission channel of FIG. 1;

FIG. 3B shows an equivalent circuit of the switch of FIG. 3A underturn-on conditions;

FIG. 4 shows in greater detail a block comprised within the transmissionchannel of FIG. 1;

FIG. 5 schematically shows a transmission channel, for example forultrasound applications, realised according to an embodiment;

FIG. 6 schematically shows an embodiment of a clamping circuit comprisedwithin the transmission channel of FIG. 5;

FIG. 7A shows in greater detail an embodiment of a switching circuitcomprised within the transmission channel of FIG. 5; and

FIG. 7B shows an equivalent circuit of the switching circuit of FIG. 7Aaccording to turning-on conditions.

DETAILED DESCRIPTION

In the following description, numerous specific details are given toprovide a thorough understanding of embodiments. The embodiments can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations, such as, for example, high-voltagetransistors, diodes, drivers, etc., are not shown or described in detailto avoid obscuring aspects of the embodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” “according to an embodiment” or “in an embodiment” andsimilar phrases in various places throughout this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

The headings provided herein are for convenience only and do notinterpret the scope or meaning of the embodiments.

With reference to these figures, and in particular to FIGS. 5 and 6, atransmission channel for ultrasound applications is described, beingglobally indicated with 100.

In its more general form, the transmission channel 100 is of the typecomprising at least one high voltage buffer block 4 in turn comprisingbuffer transistors and respective buffer diodes, being electricallycoupled between respective voltage reference terminals. The buffertransistors are also connected to a clamping circuit 10, in turncomprising clamping transistors connected to internal nodes of thetransmission channel 100 through diodes connected to prevent the bodydiodes of the clamping transistors from conducting. Moreover, thetransmission channel 100 comprises at least one reset circuit 20comprising diodes and being electrically coupled between circuit nodesof the high voltage buffer block 4 and of the clamping circuit 10, saidcircuit nodes being in correspondence with conduction terminals of thetransistors comprised into the high voltage buffer block 4 and into theclamping circuit 10.

According to an embodiment, the transmission channel 100 comprises:

-   -   a clamping circuit 10 connected to a clamp voltage reference        terminal PGND and comprising a clamping core 11 connected to a        first output terminal HVout and having a clamp central node XC        connected to a buffer central node XB of a high voltage buffer        block 4;    -   a reset circuit 20, comprising diodes and coupled to the inner        nodes of the high voltage buffer block 4 and of the clamping        circuit 10 that are to be correctly repositioned or biased, as        well as    -   a switching circuit 30 electrically coupled between a connection        terminal Xdcr to a load and a second output terminal LVout of        the transmission channel 100.

More in detail, the reset circuit 20 is connected to the interconnectioncircuit nodes between the transistors and the buffer diodes of the highvoltage buffer block 4 and to a first and to a second clamp circuitnode, XC1 and XC2, of the clamping circuit 10. In particular, the resetcircuit 20 is connected:

-   -   to a first memory node XME1, between the first buffer transistor        MB1 and the first buffer diode DB1;    -   to a second memory node XME2, between the second buffer        transistor MB2 and the second buffer diode DB2;    -   to a third memory node XME3, between the third buffer transistor        MB3and the third buffer diode DB3;    -   to a fourth memory node XME4, between the fourth buffer        transistor MB4and the fourth buffer diode DB4;    -   to the first clamp circuit node XC1; and    -   to the second clamp circuit node XC2.

As previously seen, the high voltage buffer block 4 comprises at leastone first branch in turn including the first buffer transistor MB1 andthe first buffer diode DB1, being electrically coupled, in series toeach other, between a first higher voltage reference terminal HVP0 andthe buffer central node XB and interconnected in correspondence with thefirst memory node XME1, as well as the second buffer diode DB2 and thesecond buffer transistor MB2, being electrically coupled, in series toeach other, between the buffer central node XB and a first lower voltagereference terminal HVM0 and interconnected in correspondence with thesecond memory node XME2.

The high voltage buffer block 4 also has a first OUTB1 and a secondoutput terminal OUTB2 respectively connected to a first INC1 and to asecond input terminal INC2 of the clamping circuit 10.

The reset circuit 20 comprises respective memory nodes beingelectrically coupled between these circuit nodes and as illustrated atleast:

-   -   one first memory diode DME1, being electrically coupled between        the first memory node XME1 and the first clamp circuit node XC1;        and    -   one second memory diode DME2, being electrically coupled between        the second memory node XME2 and the second clamp circuit node        XC2.

As illustrated, the first memory diode DME1 has a cathode terminalconnected to the first memory node XME1 and an anode terminal connectedto the first clamp circuit node XC1. In a dual way, the second memorydiode DME2 has an anode terminal connected to the second memory nodeXME2 and a cathode terminal connected to the second clamp circuit nodeXC2.

Moreover, as previously seen, the high voltage buffer block 4 comprises,in parallel to the first branch, a second branch in turn including thethird buffer transistor MB3 and the third buffer diode DB3, beingelectrically coupled, in series to each other, between a second highervoltage reference terminal HVP1 and the buffer central node XB andinterconnected in correspondence with the third memory node XME3, aswell as the fourth buffer diode DB4 and the fourth buffer transistorMB4, being electrically coupled, in series to each other, between thebuffer central node XB and a second lower voltage reference terminalHVM1 and interconnected in correspondence with the fourth memory nodeXME4.

Further, the reset circuit 20 thus comprises:

-   -   a third memory diode DME3, being electrically coupled between        the third memory node XME3 and the first clamp circuit node XC1;        and    -   a fourth memory diode DME4, being electrically coupled between        the fourth memory node XME4 and the second clamp circuit node        XC2.

As illustrated, the third memory diode DME3 has a cathode terminalconnected to the third memory node XME3 and an anode terminal connectedto the first clamp circuit node XC1. In a dual way, the fourth memorydiode DME4 has an anode terminal connected to the fourth memory nodeXME4 and a cathode terminal connected to the second clamp circuit nodeXC2.

The memory diodes DME1, DME2, DME3 and DME4 are high voltage diodes (HVdiode).

In substance, the reset circuit 20 forces all the circuit nodes it isconnected to in a neighbourhood of a value of ground reference andfacilitates the transmission channel 100 restarting according tosubstantially a same condition at any pulse cycle.

It is to be noted that the memory circuit nodes correspond to the drainterminals of the corresponding buffer transistors of the high voltagebuffer block 4. Moreover, the memory diodes are connected so as to haveterminals being not homologue with the buffer diodes.

As illustrated, the first memory diode DME1 has the cathode terminalconnected to the anode terminal of the first buffer diode DB1, thesecond memory diode DME2 has the anode terminal connected to the cathodeterminal of the second buffer diode DB2, the third memory diode DME3 hasthe cathode terminal connected to the anode terminal of the third bufferdiode DB3, and the fourth memory diode DME4 has the anode terminalconnected to the cathode terminal of the fourth buffer diode DB4.

As previously seen, the high voltage buffer block 4 comprises respectivebuffer drivers connected to control terminals of the buffer transistors.

Furthermore, the transmission channel 100 comprises an anti-noise block6 being electrically coupled between the first output terminal HVout andthe connection terminal Xdcr.

As shown in greater detail in FIG. 6, the clamping circuit 10 comprisesthe clamping core 11, connected to the first output terminal HVout andin turn comprising a first and a second clamp transistor, MC1 and MC2,connected to the clamp central node XC and having respective control orgate terminals, XG1 and XG2.

These first and second clamp transistor, MC1 and MC2, have respectivefirst and second equivalent diodes, DMC1 and DMC2, also indicated in thefigure. In particular, in the example of the figure, the first clamptransistor MC1 is a high voltage N-channel MOS transistor (HV Nmos)while the second clamp transistor MC2 is a high voltage P-channel MOStransistor (HV Pmos).

The clamping core 11 also comprises a first and a second switching offtransistor, MS1 and MS2. In particular, the first switching offtransistor MS1 is electrically coupled in series to the first clamptransistor MC1 and connected to the first output terminal HVout.Moreover, the second switching off transistor MS2 is electricallycoupled in series to the second clamp transistor MC2 and also connectedto the first output terminal HVout.

These first and second switching off transistors, MS1 and MS2, haverespective first and second equivalent diodes, DMS1 and DMS2, alsoindicated in the figure. In particular, the first and second switchingoff transistors, MS1and MS2, are high voltage MOS transistors of theopposed type with respect to the clamp transistors, MC1 and MC2. In theexample of the figure, the first switching off transistor MS1 is a highvoltage P-channel MOS transistor (HV Pmos), while the second switchingoff transistor MS2 is a high voltage N-channel MOS transistor (HV Nmos).Moreover, the first equivalent or body diodes, DMS1 and DMC1, of thefirst switching off transistor MS1and of the first clamping transistorMC1, respectively, are connected in anti-series in correspondence with afirst clamp circuit node XC1. Analogously, the second equivalent or bodydiodes, DMS2 and DMC2, of the second switching off transistor MS2 and ofthe second clamping transistor MC2, respectively, are connected inanti-series in correspondence with a second clamp circuit node XC2.

These first and second switching off transistors, MS1 and MS2, are MOStransistors able to close themselves when the clamping circuit 10 isactive and to sustain positive and negative high voltages when theclamping circuit 10 is not active and the transistors are in openconfiguration, in particular also thanks to the use of a suitabledriving circuit, as it will be clarified hereafter.

Further, the clamping core 11 is then connected at the input to an inputdriver block 13 through a driving circuit 14 of the switching offtransistors MS1 and MS2, suitable for closing the first and secondswitching off transistors, MS1 and MS2 when the clamping circuit 10 isactive, as it will be clarified hereafter in the description.

The input driver block 13 is of the low voltage type and comprises afirst driver DRC1 electrically coupled between a first clamp supplyvoltage reference terminal and a second clamp supply voltage referenceterminal, higher VDD_P and lower VDD_M, respectively, and having anoutput terminal connected to the first control terminal XG1 of the firstclamp transistor MC1 as well as a second driver DRC2, in turnelectrically coupled between the first and second clamp supply voltagereferences, higher VDD_P and lower VDD_M, respectively, and having anoutput terminal connected to the second control terminal XG2 of thesecond clamp transistor MC2.

The driving circuit 14 comprises a first and a second drivingtransistor, M1 and M2, electrically coupled, in a crossed way, betweenthe control terminals of the first and second clamp transistors, MC1 andMC2, and of the first and second switching off transistors, MS1 and MS2.

In particular, the first driving transistor M1 is electrically coupledbetween the first control terminal XG1 of the first clamp transistor MC1and a control or gate terminal XS2 of the second driving transistor MS2,while the second driving transistor M2 is electrically coupled between acontrol or gate terminal XS1 of the first driving transistor MS1 and thecontrol terminal XG2 of the second clamp transistor MC2.

Furthermore, the first and the second driving transistor, M1 and M2,have respective control or gate terminals, X1 and X2, connected to theclamp central node XC.

In particular, the first and second driving transistors, M1 and M2, arehigh voltage MOS transistors of a similar type with respect to theswitching off transistors MS1 and MS2. In particular, in the example ofthe figure, the first driving transistor M1 is a high voltage P-channelMOS transistor (HV Pmos) while the second driving transistor M2 is ahigh voltage N-channel MOS transistor (HV Nmos). These first and seconddriving transistors, M1 and M2, have respective first and secondequivalent diodes, DM1 and DM2, as indicated in the figure.

In this way, the driving circuit 14 ensures the switching off of theswitching off transistors MS1 and MS2. In particular, the drivingcircuit 14 drives at high voltage the first and second switching offtransistors, MS1 and MS2, forcing their closure during the clampingstep, while the first and second clamp transistors, MC1 and MC2, aredriven at low voltage (with voltage that varies between 0 and 3 V)directly by the input driver block 13.

The first output terminal HVout is thus forced to ground and kept toground thanks to the switching off transistors MS1 and MS2 driven by thedriving circuit 14, in particular at the turning-on and switching off ofthe first and of the second switching off transistors MS1 and MS2 by thefirst and second driving transistors M1 and M2.

It is to be noted that, during the clamping step, also with a high loadvalue (and according to receiving conditions in case of application to atransmission channel), the current flows through the channel of thetransistors of the clamping circuit 10 without charging the intrinsicdiodes DMS1 and DMS2 of the switching off transistors MS1 and MS2,overcoming in this way the problems seen in relation to the prior art.In particular, the load current does not flow through the junction ofthe equivalent diodes DMS1 and DMS2 of the switching off transistors MS1and MS2, but through their channel, avoiding to charge possible junctioncapacitances that would be present with the diodes of the circuit shownin FIG. 4.

The transmission channel 100 also comprises a switching circuit 30 inturn including at least one first switching transistor MSW1and a secondswitching transistor MSW2 electrically coupled, in series to each other,between the connection terminal Xdcr and the second output terminalLVout. The switching circuit 30 is in particular used as switchingcircuit between a reception mode and a transmission mode of thistransmission channel 100 and transfers, when on, a low voltage signalbeing at the output of the anti-noise block 6 of the transmissionchannel 100 towards the second output terminal LVout.

In the example of FIG. 7A, the first switching transistor MSW1 is a highvoltage P-channel MOS transistor (HV Pmos) while the second switchingtransistor MSW2 is a high voltage N-channel MOS transistor (HV Nmos). InFIG. 7A also the parasite or body diodes of these transistors areindicated, respectively DSW1 and DSW2, being connected in antiseries incorrespondence with a first inner circuit node XW1.

In an embodiment, the switching circuit 30 comprises at least onebootstrap circuit 31 connected to a first control or gate terminal XGW1and to a second control or gate terminal XGW2 of the first switchingtransistor MSW1 and of the second switching transistor MSW2,respectively.

The bootstrap circuit 31 is also connected, in correspondence with afirst bootstrap node XBW1 and with a second bootstrap node XBW2, to afirst voltage reference terminal VDD_M and to a second voltage referenceterminal VDD_P, in particular a supply one.

The bootstrap circuit 31 comprises at least one first biasing generatorG1 being electrically coupled between the first control terminal XGW1and the first bootstrap node XBW1, as well as a second biasing generatorG2 electrically coupled between the second bootstrap node XBW2 and thesecond control terminal XGW2. These first and second biasing generators,G1 and G2, supply respective first and second biasing currents, Ib1 andIb2 and have respective first and second parasite capacitances, Cgen1and Cgen2, that are the parasite capacitances of the bootstrap circuit31, respectively electrically coupled between the first control terminalXGW1 and the first bootstrap node XBW1 and between the second controlterminal XGW2 and the second bootstrap node XBW2.

These first and second parasite capacitances, Cgen1 and Cgen2, may havemuch lower capacitance than respective first and second gate-sourcecapacitances, Csw1 and Csw2, of the first and second switchingtransistor, MSW1 and MSW2. For example, these first and second parasitecapacitances, Cgen1 and Cgen2, have a capacitive value of at least oneorder of magnitude, preferably in some embodiments of some orders ofmagnitude, for example three orders of magnitude, lower than the firstand second gate-source capacitances, Csw1 and Csw2.

For example, the first parasite capacitance Cgen1 has capacitive valueof at least one order of magnitude lower than the first gate-sourcecapacitance Csw1 of the first switching transistor MSW1 and the secondparasite capacitance Cgen2 has capacitive value of at least one order ofmagnitude lower that the second gate-source capacitance Csw2 of thesecond switching transistor MSW2.

The bootstrap circuit 31 also comprises a first bootstrap transistorMBW1 being electrically coupled, in series to a first bootstrapresistive element RBW1, between the first control terminal XGW1 of thefirst switching transistor MSW1 and the second bootstrap node XBW2. Thefirst bootstrap transistor MBW1 also has a control or gate terminalconnected to the first inner circuit node XW1 of the switching circuit30, corresponding to a source terminal of the first switching transistorMSW1.

Similarly, the bootstrap circuit 31 comprises a second bootstraptransistor MBW2 being electrically coupled, in series to a secondbootstrap resistive element RBW2, between the second control terminalXGW2 of the second switching transistor MSW2 and the first bootstrapnode XBW1. The second bootstrap transistor MBW2 also has a control orgate terminal connected to a second inner circuit node XW2 of theswitching circuit 30, corresponding to a source terminal of the secondswitching transistor MSW2.

In the example of the figure, the first bootstrap transistor MBW1 is alow voltage N-channel MOS transistor (LV Nmos) while the secondbootstrap transistor MBW2 is a low voltage P-channel MOS transistor (LVPmos).

The first biasing generator G1 is a current generator suitable forsupplying such a current Ib1 that the voltage developed by this currentIb1 flowing through the first bootstrap transistor MBW1 and the firstbootstrap resistive element RBW1 is able to turn on the first switchingtransistor MSW1. The same way, the second biasing generator G2 is acurrent generator suitable for supplying such a current Ib2 that thevoltage developed by this current Ib2 flowing through the secondbootstrap transistor MBW2 and the second bootstrap resistive elementRBW2 is able to turn on the second switching transistor MSW2.

According to working or turn-on conditions of the switching circuit 30,the same behaves like its equivalent circuit shown in FIG. 7B.

For example, the gate terminals of the switching transistors MSW1 andMSW2 are both connected to a node in voltage, schematised in the Figureas connected to the ground GND and these transistors behave asrespective resistances RSW1 and RSW2, that are electrically coupledbetween the connection terminal Xdcr and the output terminal LVout ofthe transmission channel 1 (the output terminal LVout coinciding withthe second inner circuit node XW2) and interconnected in correspondencewith the first inner circuit node XW1.

According to these conditions, thanks to the presence of the bootstrapcircuit 31 and of its biasing generators G1 and G2, the firstgate-source capacitance Csw1 of the first switching transistor MSW1 iselectrically coupled, in series to the first parasite capacitance Cgen1of the first biasing generator G1 between the first inner circuit nodeXW1 and ground GND, while the second gate-source capacitance Csw2 of thesecond switching transistor MSW2 is electrically coupled, in series tothe second parasite capacitance Cgen2 of the second biasing generator G2between the second inner circuit node XW2 and ground GND.

In this way, the total parasite capacitance (enclosed by a dotted circlein FIG. 7B) is reduced with respect to the known circuits, decreasing inconsequence the undesired mitigation of the signal at the input of theswitching circuit 30 itself, in particular applied to the connectionterminal Xdcr and transmitted towards the second output terminal LVout.

According to an embodiment, the transmission channel 100 is for exampleused for the driving of a piezoelectric transducer for ultrasoundapplications.

In an embodiment, the transmission channel 100, thanks to the presenceof the clamping circuit as above indicated facilitates more accurateclamping of the same to a voltage reference, for example to a groundGND, also when a load of high value is present, eliminating or reducingmalfunctions connected to the load of the junction capacitances of thediodes of the known circuits.

For example, when the clamping circuit is turned on, the value of thevoltage being on the connection terminal Xdcr reaches a value equal tothe ground value GND plus or minus a diode voltage, improving theperformances of second harmonic especially at low supply voltages.

Furthermore, a leakage current during a receiving step of thetransmission channel according an embodiment of the clamping circuit isconveyed towards the ground reference terminal GND preventing the firstoutput terminal HVout from charging itself and overcoming in this waythe drawbacks of the circuits described in relation to the prior art.

Moreover, the reset circuit, after a clamping step realised by theclamping circuit, forces the voltage value of drain terminal of thebuffer transistors, which are high power MOS transistors, comprisedwithin the high voltage buffer block to voltage values next to a groundreference value, so that successive pulse cycles applied to thetransmission channel restart from substantially a same initialcondition.

For example, in case of ultrasound applications, this limits thedifferences between ultrasound pulse and successive ultrasound pulse.

In an embodiment of the switching circuit, transmission of a signalapplied to the connection terminal Xdcr of the transmission channel isfacilitated, this switching circuit having a reduced total parasitecapacitance when in turn-on conditions.

A technician of the field, with the aim of meeting incidental andspecific needs, will be allowed to introduce several modifications andvariations to the above described circuit, all within the scope ofprotection of the disclosure.

Some embodiments may take the form of computer program products. Forexample, according to one embodiment there is provided a computerreadable medium comprising a computer program adapted to perform one ormore of the methods described above. The medium may be a physicalstorage medium such as for example a Read Only Memory (ROM) chip, or adisk such as a Digital Versatile Disk (DVD-ROM), Compact Disk (CD-ROM),a hard disk, a memory, a network, or a portable media article to be readby an appropriate drive or via an appropriate connection, including asencoded in one or more barcodes or other related codes stored on one ormore such computer-readable mediums and being readable by an appropriatereader device.

Furthermore, in some embodiments, some or all of the systems and/ormodules may be implemented or provided in other manners, such as atleast partially in firmware and/or hardware, including, but not limitedto, one or more application-specific integrated circuits (ASICs),discrete circuitry, standard integrated circuits, controllers (e.g., byexecuting appropriate instructions, and including microcontrollersand/or embedded controllers), field-programmable gate arrays (FPGAs),complex programmable logic devices (CPLDs), etc., as well as devicesthat employ RFID technology. In some embodiments, some of the modules orcontrollers separately described herein may be combined, split intofurther modules and/or split and recombined in various manners.

The various embodiments described above can be combined to providefurther embodiments. U.S. patent application Ser. Nos. 13/538,598,13/538,802 and 13/538,840 are incorporated herein by reference in theirentireties (respectively, attorney docket numbers 852763.51701,852763.51901, and 852763.52101, each of which claims priority to ItalianApplication Nos. M109A002338, M109A002339, M109A002340 and M109A002341,all filed on Dec. 30, 2009, and to International Application Nos.PCT/EP2010/005927, PCT/EP2010/005930, PCT/EP2010/005931 andPCT/EP2010/005932, all filed on Sep. 29, 2010).

Aspects of the embodiments can be modified, if necessary to employconcepts of the various patents, applications and publications toprovide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A system, comprising: a connection terminal configured to couple to atransducer; a high-voltage output terminal; a low-voltage outputterminal; a high-voltage buffer configured to output high-voltagepulses; a voltage clamp coupled to an output of the high-voltage bufferand to the high-voltage output terminal and configured to clamp thehigh-voltage output terminal to a reference voltage between high-voltagepulses; a bias circuit coupled between the high-voltage buffer and thevoltage clamp and configured to bias the voltage clamp betweenhigh-voltage pulses; and a high-voltage switch configured to couple theconnection terminal to the low-voltage output terminal betweenhigh-voltage pulses.
 2. The system of claim 1 wherein the voltage clampcomprises: a first clamping transistor; a second clamping transistor; afirst switching off transistor coupled between the high-voltage outputterminal and the first clamping transistor; and a second switching offtransistor of the clamp coupled between the high-voltage output terminaland the second clamping transistor, wherein, the first and secondclamping transistors are high-voltage MOS transistors of complementarytypes; the first clamping transistor and the first switching offtransistor have body diodes coupled together in anti-series; and thesecond clamping transistor and the second switching off transistor havebody diodes coupled together in anti-series.
 3. The system of claim 2wherein the bias circuit comprises: a first memory diode configured tocouple to a conduction terminal of the first clamping transistor and toa conduction terminal of a first transistor of the high-voltage buffer;and a second memory diode configured to couple to a conduction terminalof the second clamping transistor of the voltage clamp and to aconduction terminal of a second transistor of the high-voltage buffer.4. The system of claim 1 wherein the bias circuit comprises: a firstmemory diode configured to couple to a conduction terminal of a firstclamp transistor of the voltage clamp and to a conduction terminal of afirst transistor of the high-voltage buffer; and a second memory diodeconfigured to couple to a conduction terminal of a second clamptransistor of the voltage clamp and to a conduction terminal of a secondtransistor of the high-voltage buffer.
 5. The system of claim 1 whereinthe high-voltage switch comprises: first and second voltage referenceterminals; first and second switching transistors electrically coupledin series to each other, and having respective body diodes coupled inanti-series, between said connection terminal and said low-voltageoutput terminal, the first switching transistor having a first controlterminal and the second switching transistor having a second controlterminal; and a bootstrap circuit connected to the first and secondcontrol terminals and to the first and second voltage references andincluding: first and second bootstrap nodes; a first parasiticcapacitance electrically coupled between said first control terminal andthe first bootstrap node; and a second parasitic capacitanceelectrically coupled between said second control terminal and the secondbootstrap node, the first and second parasitic capacitances havingcapacitance values of at least one order of magnitude lower thangate-source capacitances of said first and second switching transistors.6. The system of claim 1, comprising: an anti-noise block coupledbetween the voltage clamp and the switching circuit.
 7. The system ofclaim 2, comprising a driving circuit coupled to control terminals ofsaid first and second clamping transistors and of said first and secondswitching off transistors and configured to generate driving signals toclose said first and second switching off transistors when said clampingcircuit is active.
 8. The system of claim 7 wherein said driving circuitcomprises: a first driving transistor coupled between the controlterminal of the first clamping transistor and the control terminal ofthe second switching off transistor; and a second driving transistorcoupled between the control terminal of the second clamping transistorand the control terminal of the first switching off transistor.
 9. Thesystem of claim 8 wherein said first and second driving transistors haverespective control terminals coupled to a conduction terminal of thefirst clamping circuit and a conduction terminal of the second clampingcircuit.
 10. The system according to claim 2 wherein said first clampingtransistor is a high voltage N-channel MOS transistor and said secondclamping transistor is a high voltage P-channel MOS transistor.
 11. Thesystem of claim 1 wherein the high voltage buffer includes at least onefirst branch having a first buffer transistor and a first buffer diodecoupled in series between a first higher voltage reference terminal anda buffer central node, and a second buffer diode and a second buffertransistor coupled in series between said buffer central node and afirst lower voltage reference terminal.
 12. The system of claim 1,further comprising an ultrasound transducer coupled to the connectionterminal.
 13. The system of claim 12 wherein the ultrasound transducercomprises a piezoelectric transducer.
 14. A method, comprising:transmitting a series of high-voltage pulses through a transmissionchannel to a connection terminal; clamping, using a voltage clamp, ahigh-voltage output terminal of the transmission channel to a referencevoltage between high-voltage pulses; biasing the high-voltage clampbetween high-voltage pulses; and coupling the connection terminal to alow-voltage output terminal between high-voltage pulses.
 15. The methodof claim 14, comprising: driving a piezoelectric transducer coupled tothe connection terminal with the high-voltage pulses.
 16. The method ofclaim 15, comprising: receiving pulse echos from the piezoelectrictransducer between high-voltage pulses.
 17. The method of claim 14,comprising: driving an transducer with the high-voltage pulses;receiving pulse echos at the low-voltage output terminal between pulses;and producing an image based on the received pulse echos.
 18. The methodof claim 17 wherein the transducer is an ultrasound transducer.